Solar cell and solar cell module

Abstract

Provided is a solar cell that includes: a semiconductor substrate on which at least pn junctions are formed; a multiplicity of finger electrodes that are formed in a comb-like shape on at least one surface of the semiconductor substrate; and a plurality of bus bar electrodes that are arranged so as to be orthogonal to the lengthwise direction of the finger electrodes and are connected with the finger electrodes. This solar cell is configured so that the finger electrodes connected with one of the bus bar electrodes are separated from the finger electrodes connected with another bus bar electrode that is arranged so as to be parallel to this one of the bus bar electrodes, and ends in the lengthwise direction of adjacent two or more of the finger electrodes connected with each bus bar electrode are electrically connected with one another by auxiliary electrodes. With this configuration, while disadvantage due to disconnection is solved, a high fill factor, a high conversion efficiency, and small cell warpage are achieved, whereby the manufacturing yield is improved. Further, this does not involve increases in costs, and high long-term reliability is achieved. Thus, a solar cell module made up of the solar cells maintains high output.

The invention claimed is: 
     
       1. A method for manufacturing a solar cell comprising a semiconductor substrate having at least a pn junction formed therein, an antireflection coating layer on a light-receiving surface of the semiconductor substrate, a multiplicity of finger electrodes for current collection which are formed in comb shape on the light-receiving surface of the semiconductor substrate and bonded to the semiconductor substrate, a plurality of bus bar electrodes for collecting current from the finger electrodes which extend orthogonal to the longitudinal direction of the finger electrodes and are connected to the finger electrodes, and rear electrodes on a rear surface of the semiconductor substrate, comprising rear bus bar electrodes for current collection on the rear side without finger electrodes, the rear bus bar electrodes extending the same direction as the longitudinal direction of the bus bar electrodes on the light-receiving surface,
 wherein the semiconductor substrate is of silicon and has a thickness of less than 500 μm, 
 first finger electrodes which are joined and connected to a first bus bar electrode are spaced apart from second finger electrodes which are joined and connected to a second bus bar electrode extending parallel with the first bus bar electrode, 
 the first and second finger electrodes project from the first and second bus bar electrodes to which they are joined and connected, respectively, in opposite directions orthogonal to the first and second bus bar electrodes, and 
 at each of the opposite ends of the first and second finger electrodes projecting from the bus bar electrodes, an auxiliary electrode is joined and connected to longitudinal ends of all adjacent finger electrodes whereby longitudinal ends of all adjacent finger electrodes are electrically connected together by the auxiliary electrode: 
 the method comprising forming the antireflection coating layer on the light-receiving surface of the semiconductor substrate, screen printing a rear electrode pattern comprising the rear bus bar electrodes without finger electrodes with a rear surface conductive paste containing silver powder, glass frit, organic vehicle and organic solvent on a rear surface of the semiconductor substrate, screen printing by using a screen printing plate having an electrode pattern of the bus bar electrodes, the finger electrodes, and the auxiliary electrodes on the antireflection coating layer with a light-receiving side conductive paste containing silver powder, glass frit, organic vehicle and organic solvent, drying the rear surface conductive paste on the rear surface of the semiconductor substrate and the light-receiving side conductive paste on the light-receiving surface side of the semiconductor substrate, and firing the printed rear surface conductive paste and the printed light-receiving side conductive paste at the firing-through temperature of the light-receiving side conductive paste to form the rear bus bar electrodes without finger electrodes, the bus bar electrodes, the finger electrodes and the auxiliary electrodes of silver sintered body, wherein the finger electrodes and the auxiliary electrodes are bonded to the semiconductor substrate, each finger electrode of the multiplicity of finger electrodes has a width of 30 to 120 μm, and the auxiliary electrodes have a width of 60 to 360 μm. 
 
     
     
       2. The method of  claim 1 , wherein the electrode pattern on the screen printing step further includes 2 to 10 additional auxiliary electrodes, the 2 to 10 additional auxiliary electrodes being on each of the opposite sides of the first and second finger electrodes projecting from the bus bar electrodes, extending orthogonal to the longitudinal direction of the finger electrodes, being spaced between the longitudinal ends of the finger electrodes and the bus bar electrodes, and being joined and connected to all adjacent finger electrodes connected to the first and second bus bar electrodes, respectively, and
 the screen printing on the antireflection coating layer is conducted by using the screen printing plate having said electrode pattern of the bus bar electrodes, the finger electrodes, the auxiliary electrodes and the 2 to 10 additional auxiliary electrodes at one time. 
 
     
     
       3. The method of  claim 2  wherein said additional 2 to 10 auxiliary electrodes are equally spaced between the longitudinal ends of the finger electrodes and the bus bar electrodes. 
     
     
       4. The method of  claim 2  wherein said additional 2 to 10 auxiliary electrodes are spaced apart from each other within a distance of L/3 from the longitudinal ends of the finger electrodes, wherein L is the distance between the longitudinal end of the finger electrode and the bus bar electrode. 
     
     
       5. The method of  claim 1  wherein the spacing between the first bus bar electrode and the second bus bar electrode is 20 to 100 mm. 
     
     
       6. The method of  claim 1  wherein the first finger electrodes are not joined to the second finger electrodes. 
     
     
       7. The method of  claim 2  in which the screen printing direction is set parallel to the finger electrodes and orthogonal to the bus bar electrodes and auxiliary electrodes. 
     
     
       8. The method of  claim 1  wherein the auxiliary electrode is a sintered body connected to the ends of the finger electrodes, whereby the adhesive strength of the finger electrode end is improved to prevent the finger electrode from peeling during service. 
     
     
       9. The method of  claim 1 , wherein a ratio of the line width of the auxiliary electrode to the line width of one of the finger electrodes is from 0.5 to 8.0. 
     
     
       10. The method of  claim 1 , wherein the auxiliary electrode is a sintered body connected to the ends of the finger electrodes, whereby the adhesive strength of the finger electrode end is improved to prevent the finger electrode end from peeling from the semiconductor substrate upon thermal shrinkage after firing. 
     
     
       11. The method of  claim 1  further comprising before the step of drying and firing the printed rear surface conductive paste of the rear electrode pattern and the printed light-receiving side conductive paste on the antireflection coating layer,
 a step of screen printing another rear electrode pattern with a paste obtained by mixing aluminum powder with an organic binder in a region except on the rear bus bar electrode pattern of the rear surface of the semiconductor substrate after the screen printing step of the rear surface and before the screen printing step of the light-receiving side, 
 wherein the paste of the another rear electrode pattern is dried and fired with the drying and firing step of the rear surface conductive paste on the rear surface of the semiconductor substrate and the light-receiving side conductive paste on the light-receiving surface side of the semiconductor substrate. 
 
     
     
       12. The method of  claim 1 , wherein the semiconductor substrate of silicon has a thickness of 300 μm or less. 
     
     
       13. The method of  claim 1 , wherein the semiconductor substrate of silicon has a thickness of 250 μm or less. 
     
     
       14. The method of  claim 1 , wherein the method is for mitigating the warpage of solar cell, wherein the solar cell has a warpage of 0.5 mm or less, when the semiconductor substrate of silicon is 15 cm squares and 250 μm thick.